The present invention generally relates to wireless communication networks, and particularly relates to scheduling calls based on frame-offset selection.
The Third Generation Partnership Project 2 (3GPP2), a partnership consisting of five telecommunication standards bodies, establishes Code Division Multiple Access (CDMA) standards for wireless communication networks. There are several established CDMA standards, two of which are IS-95 and IS-2000 or cdma2000. Wireless communication networks operable in accordance with IS-95 or IS-2000 Revisions A and B are capable of supporting (a) calls established over dedicated channels such as fundamental channels and dedicated control channels and (b) calls established over a supplemental channel (hereinafter “SCH”). As used herein, a fundicated channel (“FC”) comprises a fundamental channel, a dedicated control channel, or both fundamental and dedicated control channels. Calls established over the FC (“FC calls”) are typically, but not necessarily, voice calls, and calls established over the SCH (“SCH calls”) are typically data calls having a data rate rarely exceeding 300 kbps. To satisfy the growing demand for high-speed wireless data services at rates beyond 300 kbps, IS-2000 revisions C and D were established and are backward compatible with previous revisions. Revisions C and D are also known as 1xEV-DV, referring to 1 carrier radio transmission technology Evolution for high speed integrated Voice and Data. In accordance therewith, a new channel—a Packet Data Channel (hereinafter “PDCH”)—is introduced to support high-speed wireless packet data transmission on the forward link from the network to the mobile station and also on the reverse link from the mobile station to the network. As apparent from its name, the PDCH is a packet switched channel that can be used to support more than one mobile station. More specifically, the PDCH can be shared among a potentially large plurality of packet data users to provide high-speed packet data services to the users sharing such channel.
Because revisions C and D are backward compatible with previous revisions A and B, 1xEV-DV wireless communication networks are capable of supporting (1) traditional voice and data calls established over FCs and SCHs as well as (2) data calls established over a time shared high-speed packet data channel such as the PDCH. In practice, FC calls will have higher priority than SCH calls, which in turn will have higher priority than calls established over the PDCH (“PDCH calls”). Therefore, radio resources such as power and Walsh codes will be given to calls based on the following prioritized order: calls established over the FC; calls established over the SCH and calls established over the PDCH.
cdma2000 networks generally maintain an overall system timing based on 20-millisecond (ms) time intervals and frames. Each 20 ms frame is divided into sixteen power control groups (PCGs) or sixteen 1.25 ms time intervals and the beginning of each PCG or 1.25 ms time interval is known as a frame offset as illustrated in FIG. 1. If there are incoming FC and SCH calls, the network schedules such calls by randomly selecting a frame offset for each incoming FC or SCH call, using such selected frame offset to establish frame timing for communicating with the respective mobile station and also informing the respective mobile station to use the same selected frame offset to establish frame timing for communicating with the network. On the forward radio link, the network transmits traffic frames to the mobile stations associated with FC and SCH calls at various frame offsets as illustrated in FIG. 2. Likewise, such mobile stations also transmit traffic frames to the network at various times on the reverse radio link. Accordingly, the network's call processing load is more evenly distributed within each 20 ms time interval.
This conventional method of synchronizing traffic frames for different users at different frame offsets to achieve a more uniform distribution of call processing load does not necessarily complement all aspects of network operation defined in the newer cdma2000 standards. For example, 1xEV-DV wireless communication networks could also support calls established over the high speed PDCH. To do so, the 1xEV-DV wireless communication network uses radio resources such as power and Walsh codes that are remained or left over after calls established over FC and SCH have been supported since FC and SCH calls are prioritized higher than PDCH calls as discussed above. Such “leftover” radio resources could dynamically change every PCG or every 1.25 ms as existing FC/SCH calls are disconnected from the network or incoming FC/SCH calls are being supported by the network. As a result, the fluctuation associated with leftover radio resources prevent the network from efficiently using such leftover radio resources to better support PDCH calls as further explained below.
FIG. 3 illustrates a graph showing a waveform representing the network's prediction of how its power might be used to support FC and SCH calls starting at t0. Such prediction is necessary for the network to further estimate how much of the leftover power it should use to support PDCH calls on the forward radio link. More specifically, shaded area 2 below the waveform represents power that the network is expecting to be used for supporting FC and SCH calls while the area above the waveform and below Pmax represents leftover power that could be used to support calls established over PDCH. Assuming the network needs to transmit data from t1 to t3 to a mobile station having an active PDCH call with the network, (Pmax−P1) is the maximum leftover power that the network could use to support such transmission even though the estimated leftover power at t3, for example, is greater than (Pmax−P1). Thus, one can see areas 4, 6 and 8 that are above the waveform and below the dotted line represent leftover power that could not be used to support any calls because if the network tries to use more power than (Pmax−P1) to support the PDCH call such as using (Pmax−P0), the network would not have enough power to support FC and SCH calls, which take precedent over PDCH call, especially for example at t2 when P1 will be required to support the FC and SCH calls. Accordingly, current networks fail to efficiently use leftover radio resources to support PDCH calls since some of the leftover power resources cannot be used and thus are wasted.
Likewise, current networks also do not efficiently use leftover Walsh codes resources to support PDCH calls. As FC and SCH calls occupy more Walsh codes with the arrival of incoming calls or abandon Walsh codes as current calls established over such channels are disconnected from the network, the number of leftover Walsh codes that are available to support PDCH calls can change every 1.25 ms or PCG. If there are newly available Walsh codes that could be used to support PDCH calls, the network could not use such newly available Walsh codes for mutli-coding the PDCH because the mobile stations having PDCH calls with the network are not yet aware of such newly available Walsh codes and thus would not be able to demodulate the information sent by the network correctly. To take advantage of such newly available Walsh codes for multi-coding, the network needs to send out a Walsh Mask Broadcast (WMB) message to inform the mobile stations regarding their availability. Sending such WMB message requires 21 bits and thus networks are preferably configured so as to minimize the number of WMB message transmissions to save overhead resources. Regardless, until the network sends out such WMB message, the newly available Walsh codes could not be used.